SIAM - sediment impact analysis methods

Abstract

The Sediment Impact Analysis Methods (SIAM) techniques provide a framework to assemble and draw quantitative sediment load and morphologic change conclusions from hydrologic, hydraulic, and morphologic information describing the flow of sediment through a watershed. SIAM conceptualizes a basin as a network of linked reaches that store, release, and convey sediment from watershed sources and channel boundaries. The procedures non-numerically assess channel stability and the movement of material from a systems approach, while maintaining linkages between local morphologic changes, sediment sources, and network evolution. SIAM channel networks can include non-cohesive, cohesive, armored, and bedrock reaches. Inputs of sediment sources, hydrology, hydraulics, and transport potential provide information on the materials entering the system and how those materials move through individual reaches as wash load, bed material load, and transitioning material. SIAM synthesizes how sediment sources and reaches interact both locally and across the network. Results include a local balance to determine potential areas of channel instability, sediment source tracking to indicate where potentially problematic material originates, and energy-based methods to provide estimates of channel adjustment. Each concept is applied to a hypothetical scenario to demonstrate model behavior and then to Hickahala Basin, Mississippi, for a field application. Results matched prior studies for identifying areas of channel stability and the linkages to sediment sources. Energy methods represented ranges of individual channel adjustment and equilibrium conditions with order of magnitude accuracy. Further work is required for computations predicting net aggradation or degradation from interactions between multiple adjusting unstable reaches. SIAM quantitatively examines channel instability at the fundamental level of sediment balance rather than from the perspective of morphologic change. At the reach scale, morphologic change results from sediment imbalance. Assessment of stability at the sediment balance level may be more effective for design purposes than using an estimated morphologic change approach. The model produces a sediment analysis and design process that is more detailed than a qualitative assessment but less complicated than a numerical mobile boundary model. SIAM is a design and analysis tool for the existing condition, not a predictive tool for future conditions.